162 Ground improvement by deep vibratory methods
In order to compute the ULS of the slope stability, different design approaches
(DAs) are allowed. In Britain, DA 1 is used, where two combinations of sets
of partial safety factors need to be investigated. Alternatively, in Germany,
DA 3 is utilized in which the actions—here the life load (e.g., from traffic)
at the top of the embankment—are used as design (factored) values and the
resistance in the resulting shear plane is calculated from designing (factored)
shear parameters of the soil. In the above example all characteristic shear
parameters φ avg and c avg , respectively, of Table 4.8 were factored according
to the following equation:
′
=
′
(
) =
ϕ
ϕ
γ γ
ϕ
ϕ
avg,d
avg,k
arctan tan
;
.
1 25
(4.74)
′
= ′
=
c
c
c
c
avg,d
avg,k γ γ
;
.
1 25
(4.75)
The unit weight of the soil material as being permanent is factored by
γ G = 1.0 and thus remains unchanged, while the unfavorable life load is
factored by γ Q = 1.3 to p d = 26 kPa. From a new analysis with the above
parameters it can be shown that
E
R
d
d
=
=
≤
166 4
277 4
0 6 1
.
.
.
.
MNm
MNm
(4.76)
4.6.3 Bearing capacity calculation of single
footings on stone columns
The construction of a new steel framed industrial hall with a base area of
228 × 144 m and a height of 12 m makes ground improvement measures necessary, since the subsoil is unsuitable for carrying the high structural loads.
Below a relatively old upto 4.5-m thick layer of fill consisting primarily of
cohesive material follows soft marl with depths ranging to 15 m and more,
which is underlain by dense sand. The foundation of the structure consists
of single footings arranged in a regular pattern of 24 × 12 m, with footing
areas between 3.5 × 3.5 m and 5.8 × 5.8 m depending on the applied loading.
The ground improvement is achieved by arranging vibro replacement
stone columns below the structure with diameters of generally 0.7 m. Below
the slab, the stone columns are arranged in a square pattern of 3 × 3 m,
and underneath the footing groups of 9, 13, and 25 stone columns are constructed, depending on footing size and load to be carried.
In the following, this project will also serve as an example to illustrate the
way of assessing the bearing capacity of single footings founded on vibro
stone columns in the ULS. Figure 4.31 shows the soil profile and the plan
view of a highly loaded 5.8 × 5.8 m footing carrying a maximum design
load of V d = 10.1 MN. Table 4.9 summarizes the soil parameters necessary for this bearing capacity calculation. The settlement improvement
In order to compute the ULS of the slope stability, different design approaches
(DAs) are allowed. In Britain, DA 1 is used, where two combinations of sets
of partial safety factors need to be investigated. Alternatively, in Germany,
DA 3 is utilized in which the actions—here the life load (e.g., from traffic)
at the top of the embankment—are used as design (factored) values and the
resistance in the resulting shear plane is calculated from designing (factored)
shear parameters of the soil. In the above example all characteristic shear
parameters φ avg and c avg , respectively, of Table 4.8 were factored according
to the following equation:
′
=
′
(
) =
ϕ
ϕ
γ γ
ϕ
ϕ
avg,d
avg,k
arctan tan
;
.
1 25
(4.74)
′
= ′
=
c
c
c
c
avg,d
avg,k γ γ
;
.
1 25
(4.75)
The unit weight of the soil material as being permanent is factored by
γ G = 1.0 and thus remains unchanged, while the unfavorable life load is
factored by γ Q = 1.3 to p d = 26 kPa. From a new analysis with the above
parameters it can be shown that
E
R
d
d
=
=
≤
166 4
277 4
0 6 1
.
.
.
.
MNm
MNm
(4.76)
4.6.3 Bearing capacity calculation of single
footings on stone columns
The construction of a new steel framed industrial hall with a base area of
228 × 144 m and a height of 12 m makes ground improvement measures necessary, since the subsoil is unsuitable for carrying the high structural loads.
Below a relatively old upto 4.5-m thick layer of fill consisting primarily of
cohesive material follows soft marl with depths ranging to 15 m and more,
which is underlain by dense sand. The foundation of the structure consists
of single footings arranged in a regular pattern of 24 × 12 m, with footing
areas between 3.5 × 3.5 m and 5.8 × 5.8 m depending on the applied loading.
The ground improvement is achieved by arranging vibro replacement
stone columns below the structure with diameters of generally 0.7 m. Below
the slab, the stone columns are arranged in a square pattern of 3 × 3 m,
and underneath the footing groups of 9, 13, and 25 stone columns are constructed, depending on footing size and load to be carried.
In the following, this project will also serve as an example to illustrate the
way of assessing the bearing capacity of single footings founded on vibro
stone columns in the ULS. Figure 4.31 shows the soil profile and the plan
view of a highly loaded 5.8 × 5.8 m footing carrying a maximum design
load of V d = 10.1 MN. Table 4.9 summarizes the soil parameters necessary for this bearing capacity calculation. The settlement improvement